The Guidebook lists it as "must be ambulatory".
It includes narrow tunnels, bumpy paths, caves, rope and plank bridges and is really very poorly accessible. You get there on a raft, which may be difficult to get a wheelchair on (no ECVs and I think no power wheelchairs). Most people with wheelchairs who do go there just stay at the dock. There is a restaurant (Aunt Polly's) which may or may not be open.